.\" Copyright (c) 1988, 1990, 1993, 1994
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. All advertising materials mentioning features or use of this software
.\" must display the following acknowledgement:
.\" This product includes software developed by the University of
.\" California, Berkeley and its contributors.
.\" 4. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)su.1 8.2 (Berkeley) 4/18/94
.\" $FreeBSD: src/usr.bin/su/su.1,v 1.40 2007/07/24 06:41:07 delphij Exp $
.\"
.Dd September 13, 2006
.Dt SU 1
.Os
.Sh NAME
.Nm su
.Nd substitute user identity
.Sh SYNOPSIS
.Nm
.Op Fl
.Op Fl flm
.Op Ar login Op Ar args
.Sh DESCRIPTION
The
.Nm
utility requests appropriate user credentials via PAM
and switches to that user ID
(the default user is the superuser).
A shell is then executed.
.Pp
PAM is used to set the policy
.Xr su 1
will use.
In particular, by default only users in the
.Dq Li admin
or
.Dq Li wheel
groups can switch to UID 0
.Pq Dq Li root .
This group requirement may be changed by modifying the
.Dq Li pam_group
section of
.Pa /etc/pam.d/su .
See
.Xr pam_group 8
for details on how to modify this setting.
.Pp
By default, the environment is unmodified with the exception of
.Ev USER ,
.Ev HOME ,
and
.Ev SHELL .
.Ev HOME
and
.Ev SHELL
are set to the target login's default values.
.Ev USER
is set to the target login, unless the target login has a user ID of 0,
in which case it is unmodified.
The invoked shell is the one belonging to the target login.
This is the traditional behavior of
.Nm .
.Pp
The options are as follows:
.Bl -tag -width Ds
.It Fl f
If the invoked shell is
.Xr csh 1 ,
this option prevents it from reading the
.Dq Pa .cshrc
file.
.It Fl l
Simulate a full login.
The environment is discarded except for
.Ev HOME ,
.Ev SHELL ,
.Ev PATH ,
.Ev TERM ,
and
.Ev USER .
.Ev HOME
and
.Ev SHELL
are modified as above.
.Ev USER
is set to the target login.
.Ev PATH
is set to
.Dq Pa /bin:/usr/bin .
.Ev TERM
is imported from your current environment.
The invoked shell is the target login's, and
.Nm
will change directory to the target login's home directory.
.It Fl
(no letter) The same as
.Fl l .
.It Fl m
Leave the environment unmodified.
The invoked shell is your login shell, and no directory changes are made.
As a security precaution, if the target user's shell is a non-standard
shell (as defined by
.Xr getusershell 3 )
and the caller's real uid is
non-zero,
.Nm
will fail.
.El
.Pp
The
.Fl l
(or
.Fl )
and
.Fl m
options are mutually exclusive; the last one specified
overrides any previous ones.
.Pp
If the optional
.Ar args
are provided on the command line, they are passed to the login shell of
the target login.
Note that all command line arguments before the target login name are
processed by
.Nm
itself, everything after the target login name gets passed to the login
shell.
.Pp
By default (unless the prompt is reset by a startup file) the super-user
prompt is set to
.Dq Sy \&#
to remind one of its awesome power.
.Sh ENVIRONMENT
Environment variables used by
.Nm :
.Bl -tag -width HOME
.It Ev HOME
Default home directory of real user ID unless modified as
specified above.
.It Ev PATH
Default search path of real user ID unless modified as specified above.
.It Ev TERM
Provides terminal type which may be retained for the substituted
user ID.
.It Ev USER
The user ID is always the effective ID (the target user ID) after an
.Nm
unless the user ID is 0 (root).
.El
.Sh FILES
.Bl -tag -width ".Pa /etc/pam.d/su" -compact
.It Pa /etc/pam.d/su
PAM configuration for
.Nm .
.El
.Sh EXAMPLES
.Bl -tag -width 5n -compact
.It Li "su man -c catman"
Runs the command
.Li catman
as user
.Li man .
You will be asked for man's password unless your real UID is 0.
.It Li "su man -c 'catman /usr/share/man /usr/local/man'"
Same as above, but the target command consists of more than a
single word and hence is quoted for use with the
.Fl c
option being passed to the shell.
(Most shells expect the argument to
.Fl c
to be a single word).
.It Li "su -l foo"
Simulate a login for user foo.
.It Li "su - foo"
Same as above.
.It Li "su -"
Simulate a login for root.
.El
.Sh SEE ALSO
.Xr csh 1 ,
.Xr sh 1 ,
.Xr group 5 ,
.Xr passwd 5 ,
.Xr environ 7 ,
.Xr pam_group 8
.Sh HISTORY
A
.Nm
command appeared in
.At v1 .